Wafer polishing apparatus for adjusting height of wheel tip

ABSTRACT

In a wafer polishing apparatus, the height of the wheel tip can be adjusted. The wafer polishing apparatus includes a wheel tip constructed and arranged to be in direct contact with a wafer; a spindle shaft configured to receive power to enable rotation of the wheel tip; a wheel shank positioned at a lower part of the spindle shaft and supporting the wheel tip, the wheel tip not being directly fixed thereto; and a moving shaft having a first side on which the wheel tip is mounted and an opposite side to which the spindle shaft is connected, and relatively movable with respect to the spindle shaft.

PRIORITY STATEMENT

This application claims the benefit of priority under 35 U.S.C. §119from Korean Patent Application No. 10-2009-0113496, filed on Nov. 23,2009, the contents of which are hereby incorporated herein by referencein their entirety.

BACKGROUND

1. Field

Example embodiments relate to a wafer polishing apparatus for adjustinga height of a wheel tip.

2. Description of Related Art

In the manufacturing of semiconductor devices, during one of the steps,the thickness of a semiconductor wafer is adjusted using a waferthinning process. A conventional wafer thinning process is a waferpolishing process whereby an inactive surface of a wafer having nopatterns is mechanically polished to reduce the thickness thereof.

As semiconductor packages continue to undergo further size reduction sothat a compact and lightweight structure can be achieved, semiconductordevices installed in the semiconductor packages also require a compactand lightweight structure. This can be accomplished in part by adevice-thinning process, a process which continues to be furtherdeveloped.

SUMMARY

Example embodiments provide a wafer polishing apparatus capable ofmaximizing an exchange period of a wheel tip and minimizing the numberof exchanges of wheel tips through height adjustment of the wheel tip.

Example embodiments also provide a wafer polishing apparatus capable ofexchanging only a wheel tip and reusing a wheel shank by separating thewheel tip from the wheel shank.

It is to be understood that both the foregoing general description andthe following detailed description are example and explanatory and areintended to provide further explanation of the inventive concept asclaimed.

Example embodiments are directed to a wafer polishing apparatusincluding a spindle shaft rotated by a main motor; a wheel shank axiallyand rotatably coupled to the spindle shaft; a moving shaft engaged withthe spindle shaft by a gear to be rotated; and a wheel tip coupled tothe moving shaft and supported by the wheel shank, and constructed andarranged to polish a wafer.

In example embodiments, the gear may include a screw jack coupled to themoving shaft and having a female thread; and a lead screw coupled to thespindle shaft by a bearing and having a male thread.

In example embodiments, the wafer polishing apparatus may furtherinclude a step motor supported by the spindle shaft, and rotating thelead screw to straightly move the moving shaft with respect to thespindle shaft in a vertical direction.

In example embodiments, the wheel shank may include a spindle couplingpart axially coupled to the spindle shaft; and a cover part having aslide groove and in which the wheel tip is supported or slid.

In example embodiments, the moving shaft may include a connecting partto which the screw jack is integrally coupled; and a slide partextending to a lower part of the connecting part and under which thewheel tip is mounted.

In example embodiments, the spindle shaft may include a plurality ofconnecting holes extending in an axial direction thereof, and theconnecting part may be connected within the spindle shaft in a crossshape and slid along the connecting hole in a axial direction thereof.

Example embodiments are also directed to a wafer polishing apparatusincluding a rotatable spindle shaft; a wheel shank integrally fixed tothe spindle shaft; a moving shaft variably fixed to the spindle shaft;and a wheel tip detachably mounted on the moving shaft.

In example embodiments, the wheel shank may include a slide holeconfigured to conceal the wheel tip other than an exposed portion of thewheel tip in direct contact with a wafer, and the moving shaft mayinclude a slide part slid in the slide hole together with the wheel tip.

In example embodiment, the slide part may further include an attachmentgroove positioned at a first end and to which the wheel tip isdetachably attached, and the attachment groove may have an open lowerend opened so that the wheel tip can be inserted in an upward directionwith respect to a longitudinal cross-section thereof.

In example embodiments, the slide part may further include a fasteninghole passing through both sides thereof and at least the attachmentgroove, and a bolt may be fastened to the fastening hole to fix thewheel tip inserted into the attachment groove.

Example embodiments are also directed to a wafer polishing apparatusincluding: a wheel tip constructed and arranged to be in direct contactwith a wafer; a spindle shaft configured to receive power to enablerotation of the wheel tip; a wheel shank positioned at a lower part ofthe spindle shaft and supporting the wheel tip, the wheel tip not beingdirectly fixed thereto; and a moving shaft having a first side on whichthe wheel tip is mounted and a second side to which the spindle shaft isconnected, and relatively movable with respect to the spindle shaft.

In example embodiments, the wheel shank may include a spindle couplingpart coupled to the spindle shaft at an upper center thereof; and acover part configured to expose a portion of the wheel tip at a loweredge thereof.

In example embodiments, the wheel tip may have a width W of 3 mm to 4 mmand a height H of 5 mm to 15 mm, and a height H1 of the wheel tipexposed from the cover part may be maintained within a range of 1 mm to4 mm.

In example embodiments, the cover part may further include a slide holethrough which the wheel tip can vertically pass, and as the slide partis slid downward from the slide hole, a height H2 of the wheel tipconcealed by the cover part may be reduced, and the height H1 exposedfrom the cover part may be uniformly maintained within the range.

In example embodiments, the slide hole may correspond to a shape of thewheel tip, and may have a step between upper and lower parts thereof sothat a hole gap at the upper part is larger then the thickness of thewheel tip, and a hole gap at the lower part is equal to or approximateto the thickness of the wheel tip with respect to a longitudinalcross-section thereof.

In example embodiments, a vertical surface of the step may be a surfaceconfigured to support the wheel tip, and a horizontal surface of thestep may be a stopper surface to prevent the moving shaft from loweringany further.

In example embodiments, the moving shaft may include a connecting partmovably connected to the spindle shaft; and a slide part to which thewheel tip is detachably attached.

In example embodiments, the wafer polishing apparatus may furtherinclude a variable means configured to fix the moving shaft to thespindle shaft during polishing or to vary a position of the moving shaftwhen the wheel tip is worn down.

In example embodiments, the variable means may be a screw gear assembly,and the screw gear assembly may include a screw jack formed at themoving shaft; a lead screw connected to the spindle shaft and passingthrough the screw jack; and a step motor configured to rotate the leadscrew, wherein when the lead screw is rotated by the step motor, thescrew jack moves longitudinally in a vertical direction depending on arotational direction of the lead screw.

In example embodiments, the variable means may be a linear actuator, andthe linear actuator may include a piston rod extending to be connectedto the connecting part in a cross shape; and a linear step motorconfigured to move the piston rod in a longitudinal direction thereof,wherein when the linear step motor is driven, the piston rod moveslongitudinally in a vertical direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments are described in further detail below with referenceto the accompanying drawings. It should be understood that variousaspects of the drawings may have been exaggerated for providing clarity.

FIGS. 1 and 2 are longitudinal cross-sectional views schematicallydepicting a grinder including a polishing apparatus and a chuck table inaccordance with an example embodiment of the inventive concept.

FIG. 3 is a plan view illustrating the polishing apparatus in accordancewith an example embodiment of the inventive concept.

FIG. 4 is a longitudinal cross-sectional view enlarging a portion “s” ofFIG. 1 to illustrate attachment of a slide of a moving shaft to a wheeltip, and detachment of the slide from the moving shaft, in accordancewith an example embodiment of the inventive concept.

FIGS. 5 and 6 are a perspective view and a longitudinal cross-sectionalview illustrating the polishing apparatus in which a moving shaft isvaried by a screw gear assembly in accordance with an example embodimentof the inventive concept.

FIG. 7 is a cross-sectional view taken along line II-II′ of FIG. 6.

FIG. 8 is a longitudinal cross-sectional view illustrating a worn-downstate of the wheel tip in accordance with an example embodiment of theinventive concept.

FIG. 9 is a longitudinal cross-sectional view showing exchange of thewheel tip in accordance with an example embodiment of the inventiveconcept.

FIGS. 10 and 11 are longitudinal cross-sectional views showing thepolishing apparatus in which a moving shaft is varied by a linearactuator in accordance with an example embodiment of the inventiveconcept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various example embodiments will now be described more fully withreference to the accompanying drawings in which some example embodimentsare shown. In the drawings, the thicknesses of layers and regions may beexaggerated for clarity.

Detailed illustrative embodiments are disclosed herein. However,specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments. Thisinventive concept, however, may be embodied in many alternate forms andshould not be construed as limited to only example embodiments set forthherein.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the drawings and will herein be described in detail.It should be understood, however, that there is no intent to limitexample embodiments to the particular forms disclosed, but on thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of the inventiveconcept. Like numbers refer to like elements throughout the descriptionof the figures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof. Spatially relative terms,such as “beneath,” “below,” “lower,” “above,” “upper” and the like, maybe used herein for ease of description to describe one element or arelationship between a feature and another element or feature asillustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe Figures. For example, if the device in the figures is turned over,elements described as “below” or “beneath” other elements or featureswould then be oriented “above” the other elements or features. Thus, forexample, the term “below” can encompass both an orientation which isabove as well as below. The device may be otherwise oriented (rotated 90degrees or viewed or referenced at other orientations) and the spatiallyrelative descriptors used herein should be interpreted accordingly.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures). As such, variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, may be expected. Thus,example embodiments should not be construed as limited to the particularshapes of regions illustrated herein but may include deviations inshapes that result, for example, from manufacturing. For example, animplanted region illustrated as a rectangle may have rounded or curvedfeatures and/or a gradient (e.g., of implant concentration) at its edgesrather than an abrupt change from an implanted region to a non-implantedregion. Likewise, a buried region formed by implantation may result insome implantation in the region between the buried region and thesurface through which the implantation may take place. Thus, the regionsillustrated in the figures are schematic in nature and their shapes donot necessarily illustrate the actual shape of a region of a device anddo not limit the scope.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may be executed in the reverse order,depending upon the functionality/acts involved.

In order to more specifically describe example embodiments, variousaspects will be described in detail with reference to the attacheddrawings. However, the inventive concept is not limited to exampleembodiments described.

FIGS. 1 and 2 are longitudinal cross-sectional views schematicallyillustrating a grinder including a polishing apparatus and a chuck tablein accordance with an example embodiment of the inventive concept, andFIG. 3 is a plan view illustrating the polishing apparatus in accordancewith an example embodiment of the inventive concept.

Referring to FIGS. 1 and 2, a grinder 10 for machining a wafer 2 to adesired thickness includes a chuck table 12 for fixing the wafer 2, anda polishing apparatus 100 for polishing the wafer 2.

The chuck table 12 has a seating surface on which the wafer 2 is seated.The wafer 2 is disposed such that a surface thereof including activecircuitry faces the seating surface of the chuck table 12. The seatingsurface may have a vacuum suction port (not shown) for fixing the wafer2 using a vacuum. The chuck table 12 may be driven to rotate the wafer2. The rotational direction may be opposite to a rotational direction ofthe polishing apparatus 100.

The polishing apparatus 100 is disposed over the chuck table 12. Thepolishing apparatus 100 may be vertically, horizontally and reciprocallydriven by a drive part 102. In addition, the polishing apparatus 100 maybe rotated to polish the wafer 2.

The polishing apparatus 100 may include a wheel tip 110 in directcontact with the wafer 2, a main motor 120 for providing a rotationalforce to the wheel tip 110, a spindle shaft 130 connected to the mainmotor 120 and enabling rotation of the wheel tip 110, a wheel shank 140for supporting the wheel tip 110 without the wheel tip 110 beingdirectly fixed thereto, and for guiding the wheel tip 110 such that thewheel tip 110 moves downward, and being separable from the wheel tip 110upon exchange of the wheel tip 110, and a moving shaft 160 having alower part, to which the wheel tip 110 is fixed, and relatively movingwith respect to the spindle shaft 130 such that the wheel tip 110 can bemoved downward with respect to the wheel shank 140 when the wheel tip110 is worn down, while being fixed to the spindle shaft 130 during thepolishing operation.

An outer surface of the wheel tip 110, which performs the polishingoperation, may be formed by mixing diamond particles, resin particles,etc., and sintering them. A plurality of wheel tips 110 having apredetermined height H and width W may be mounted at a lower part of themoving shaft 160 at predetermined intervals. The wheel tips 110 aredisposed in a cylindrical shape when they are installed at the movingshaft 160. In example embodiments, the width W may be 3 to 4 mm and theheight H may be 5 mm or more. More specifically, the height H may be 5mm to 15 mm.

When the wheel tip 110 has a width of 3 mm to 4 mm, the height H may beset to 3 mm to 5 mm. When the height H is larger than 5 mm, the wheeltip 110 is more susceptible to deformation or breakage. However, in anembodiment where the wheel tip 110 can be supported by the wheel shank140 and the amount of exposed height H1 can be uniformly maintained, itis possible to prevent deformation or breakage of the wheel tip 110,even in a case where the height is 5 mm or more as described above.

While the wheel tip 110 may be integrally fixed to the moving shaft 160,the wheel tip 110 may be detachably attached thereto. That is, when thewheel tip 110 is detachably attached to the moving shaft 160, the wheeltip 110 can be independently separated from the moving shaft 160 whenthe wheel tip 110 is worn down, and thus, the wheel tip 110 can bereplaced with a new one.

The wheel tip 110 may be a split-type that is divided into a pluralityof bodies, or an integral type that is formed of a single body. In thecase of the split-type, a plurality of wheel tips 110 may bediscontinuously positioned in a circumferential direction atpredetermined intervals. In addition, the wheel tips 110 may be disposedalong at least two lines in a concentric manner.

The main motor 120 may be installed at one side of the driver 102 sothat the polishing apparatus 100 can be driven on the chuck table 12 ina vertical, horizontal or reciprocal direction. The main motor 120 maybe installed on the spindle shaft 130 to provide a rotational force tothe spindle shaft 130.

The spindle shaft 130 is connected to the wheel shank 140 and the movingshaft 160, and may receive power from the main motor 120 to transmit thepower to the wheel shank 140 and the moving shaft 160.

The wheel shank 140 reduces the exposed height H1 of the wheel tip 110and uniformly maintains the exposed height H1 in order to preventdeformation of, or breakage of the wheel tip 110 during a polishingprocess. A spindle-coupling part 142 may be formed on an upper surfaceof the wheel shank 140 to be coupled to the spindle shaft 130. A cover144 is formed at an edge of the wheel shank 140 to cover the wheel tip110 other than the exposed part E thereof. The cover 144 may have aslide hole 152 through which the wheel tip 110 can pass. The slide hole152 may have a shape that corresponds with that of the wheel tip 110.

The wheel tip 110 has a width W that is less than a width of a slidepart 164 of the moving shaft 160, and therefore, the slide hole 152 ofthe cover 144, which can be configured to surround the slide part 164when the wheel tip is worn (see FIG. 2), may further include ahorizontal step 156 formed at its lower part. A gap is present betweenan inner vertical sidewall 154 of the slide hole 152 and the verticalsurface of an upper portion of the wheel tip 110 within the slide hole152, and little or no gap is present between the vertical surface of thestep 156 and the lower portion of the wheel tip 110 so as to preventmovement of the wheel tip 110 relative to the slide hole 152. Inaddition, a horizontal surface of the step 156 may function as a stoppersuch that the slide part 164 cannot be lowered any further into theslide hole 152.

The moving shaft 160 may further include a connecting part 162 formed atits upper portion and slidably connected to the spindle shaft 130, andthe slide part 164 formed at its lower part, on which the wheel tip 110is mounted. The slide part 164 may correspond to the slide hole 152 tobe vertically slid within, and surrounded by, the slide hole 152.

FIG. 4 is a longitudinal cross-sectional view enlarging a portion “s” ofFIG. 1 to show attachment/detachment of a slide of a moving shaftto/from a wheel tip in accordance with an example embodiment of theinventive concept.

Referring to FIG. 4, an attachment groove 166 may be formed in an end ofthe slide part 164 to receive the wheel tip 110. The attachment groove166 may be open at its lower part so that the wheel tip 110 can beinserted and fastened in an upward direction. A fastening hole 168 maybe formed to pass through both sides of the slide part 164. Thefastening hole 168 should pass through at least the attachment groove166. When a bolt 172 is fastened to the fastening hole 168, the wheeltip 110 that is inserted into the attachment groove 166 is fixed.

The wheel tip 110 may be readily broken or deformed when excessivestress is applied thereto, because the wheel tip 110 is formed by mixingand sintering resin powder, resulting in a relatively fragile component.Therefore, a shock absorbing material 174 may be further installed inthe attachment groove 166 between the bolt 172 and the wheel tip 110.When or after the wheel tip 110 is inserted into the attachment groove166 and then the bolt 172 is fastened thereto, the shock absorbingmaterial 174 is positioned between the bolt 172 and the wheel tip 110.As a result, the stress applied to the wheel tip 110 is attenuated bythe bolt 172. Here, an inner space may be expanded such that the shockabsorbing material 174 can be installed in the attachment groove 166.

FIGS. 5 and 6 are a perspective view and a longitudinal cross-sectionalview illustrating the polishing apparatus in which the vertical positionof a moving shaft 160 relative to the wheel shank 140 is varied by ascrew gear assembly in accordance with an example embodiment of theinventive concept, and FIG. 7 is a cross-sectional view taken along lineII-II′ of FIG. 6.

Referring to FIGS. 5, 6 and 7, the connecting part 162 may have a cross(+) shape in cross-section in the spindle shaft 130 so as to increaseits durability and to improve the balance thereof. The number ofconnecting holes 132 corresponding to the number of connecting parts 162may be formed in the spindle shaft 130 so that the connecting parts 162can be slidably connected to the spindle shaft 130. For this purpose, apredetermined space for mounting the connecting part 162 may be formedin an inner upper part of the spindle shaft 130.

Referring to FIG. 6, the moving shaft 160 may further include a variablemeans for variably coupling the moving shaft 160 to the spindle shaft130. That is, the variable means can be configured to fix the connectingpart 162 of the moving shaft 160 to the spindle shaft 130 at one side,and move with respect to the spindle shaft 130 at the other side. Thevariable means may comprise, in one embodiment, a screw gear assembly180.

The screw gear assembly 180 may include a screw jack 182 installed atthe moving shaft 160, and a lead screw 184 installed at the spindleshaft 130. The screw jack 182 may include a female thread, and the leadscrew 184 may include a male thread. The lead screw 184 is installed topass through the screw jack 182. When the lead screw 184 is rotated, thescrew jack 182 moves in a vertical direction relative to the lead screw.

A step motor 186 may be fixedly installed at one side in the spindleshaft 130 to rotate the lead screw 184. Since the step motor 186 has arotator (not shown) rotated to a certain angle per input pulse providedfrom the exterior, the step motor 186 is appropriately used forautomatic control. That is, since the rotator is rotated in proportionto the number of pulse signals output from a controller (not shown), thestep motor 186 can be readily controlled by a microprocessor.

An upper end of the lead screw 184 is connected to the step motor 186,and a lower end of the lead screw 184 is connected to the spindle shaft130. The upper end of the lead screw 184 connected to the step motor 186is connected to the output rotator (not shown) of the step motor 186.The lead screw 184 may be connected to the spindle shaft 130 through abearing 188 so that the spindle shaft 130 is not rotated with the leadscrew 184.

FIG. 8 is a longitudinal cross-sectional view illustrating a worn-downstate of the wheel tip in accordance with an example embodiment of theinventive concept, and FIG. 9 is a longitudinal cross-sectional viewshowing exchange of the wheel tip in accordance with an exampleembodiment of the inventive concept.

Referring to FIGS. 8 and 9, when the lead screw 186 is rotated by thestep motor 186, only the moving shaft 160 connected to the screw jack182 moves longitudinally in a vertical direction, depending on arotational direction of the lead screw 184, and the spindle shaft 130 isnot moved by the bearing 188.

While a conventional step motor enables rotational movement, since alinear step motor enables straight movement, a linear actuator includingthe linear step motor may be used as a means for moving the movingshaft.

FIGS. 10 and 11 are longitudinal cross-sectional views showing thepolishing apparatus in which a moving shaft is varied by a linearactuator in accordance with an example embodiment of the inventiveconcept. Referring to FIGS. 10 and 11, the variable means in accordancewith another example embodiment of the inventive concept may include alinear actuator 190 for moving an object in a straight, longitudinaldirection.

The linear actuator 190 may include a piston rod 192 that extends to beconnected to the connecting part 162 of the moving shaft 160 in a crossshape, and a linear step motor 194 for moving the piston rod 192. Thepiston rod 192 may be slid straightly along one side of the spindleshaft 130 to prevent the piston rod 192 from moving horizontally whenthe moving shaft 160 is driven.

The linear actuator 190 may be an electrically-powered type forreceiving electric power, a hydraulic type for receiving hydraulicpower, or a pneumatic type for receiving pneumatic pressure. Among them,when the electrical linear step motor 194 is used as the linear actuator190, since the piston rod 192 can be straightly moved by a rotationalforce of the linear step motor 194 and driven step by step according toa control signal output from a controller (not shown), it is possible toprecisely control a moving distance of the moving shaft 160.

Hereinafter, methods of using a wafer polishing apparatus in accordancewith example embodiments of the inventive concept will be described.

Referring to FIG. 1, in a final step of a wafer manufacturing processfor forming a predetermined pattern on a wafer 2, a rear surfacepolishing process for lapping the wafer 2 to a desired thickness isperformed. The rear surface polishing process is performed to improveheat radiation of a semiconductor device bonded during a semiconductorpackage process, flatten the surface of the semiconductor device, andreduce the thickness thereof.

First, a wafer 2 is seated on a seating surface of a chuck table 12. Aninactive surface of the wafer 2 is oriented in an upward direction. Apolishing apparatus 100 is moved downward toward the chuck table 2 by adrive part 102 so that the wheel tip 110 can contact the inactivesurface of the wafer 2. When a main motor 120 is driven, the spindleshaft 130 is rotated to polish the rear surface of the wafer 2 using thewheel tip 110. Next, in a state in which the wheel tip 110 is in contactwith the inactive surface of the wafer 2, the polishing apparatus 100 ismoved horizontally by the driver 102.

Referring to FIG. 2, after repeated rear surface polishing processoperations, the wheel tip 110 is worn down. Therefore, an exposed heightH1 of the wheel tip 110 is reduced. When the exposed height H1 becomesreduced in this manner, the wheel tip 110 is lowered to maintain theexposed height H1 within a range of 1 mm to 4 mm.

Hereinafter, adjustment of the height of the wheel tip will be describedin detail.

Referring to FIG. 6, as the step motor 186 rotates, the lead screw 184is rotated. Since the spindle shaft 130 is connected to the lead screw184 by a bearing 188, the relative heights of the step motor 186 and thespindle shaft 130 are maintained in a fixed state. However, the movingshaft 160 engaged with the lead screw 184 through a screw jack 182 movesin a downward direction. That is, since the lead screw 184 is a malescrew and the screw jack 182 is a female screw, rotation of the leadscrew 184 is converted into longitudinal movement of the screw jack 182.A connecting part 162 coupled to the screw jack 182 moves to lower themoving shaft 160 to a desired distance.

Referring to FIG. 8, an operator can determine whether the exposedheight H1 of the wheel tip 110 is reduced. It can be more preciselydetermined using a distance sensor or a proximity sensor. When reductionin the exposed height H1 of the wheel tip 110 is determined using thenaked eye or the sensor, the step motor 186 can be driven to uniformlymaintain the exposed height H1 within a predetermined or desired range.In addition, referring to FIGS. 10 and 11, when a linear step motor 196is driven to straightly move a piston rod 192, the exposed height H1 canalso be uniformly maintained.

While the exposed height H1 of the wheel tip 110 can be uniformlymaintained through the height adjustment, the concealed height H2 isgradually reduced. When the length of the wheel tip 110 cannot beadjusted any further, one side of the connecting part 162 of the movingshaft 160 contacts one side of the spindle coupling part 142 of thewheel shank 140, or one side of the slide part of the moving shaft 160contacts a horizontal surface 156 of the step of the cover part 144 ofthe wheel shank 140. In particular, when a contact sensor is installedat the contact part, it is possible for an operator to readily determinean exchange time of the wheel tip 110.

Referring to FIG. 9, when it is determined that the wheel tip 110 needsto be exchanged, the moving shaft 160 is made to move in an upwarddirection. At this time, the step motor 186 is driven in a directionopposite to the rotational direction to adjust the length of the wheeltip 110. The moving shaft 160 is spaced apart from the wheel shank 140,and the wheel tip 110 is exchanged with a new one using a spacetherebetween.

When the bolt 172 is separated from the slide part 164, the wheel tip110 is removed from the attachment groove 166. A new wheel tip having aheight of 5 mm to 15 mm, for example, is installed in the attachmentgroove 166. The new wheel tip 110 is then fastened to the slide part 164using the bolt 172.

The step motor 186 is driven such that the wheel tip 110 is exposed fromthe cover part 144 to a range of 1 mm to 4 mm upon polishing. Followingproper adjustment of the length of the wheel tip 110, the polishing isperformed again.

In general, an initial polishing load may be increased after exchange ofthe wheel tip 110. In order to adjust the initial polishing load, adressing process is performed. However, when the number of exchanges ofthe wheel tips 110 is increased and the number of dressing processes isalso increased, a time for quality stabilization is consumed inproportion thereto. Since the exchange cycle of the wheel tip 110 of theembodiment is lengthened and the number of exchanges is reduced, thetime for quality stabilization can be improved.

In addition, even in a case where the wheel tip 110 is worn down, thereis no need to dispose of the wheel shank 140 together with the wheel tip110. In a state in which the wheel shank 140 is fastened, only themoving shaft 160 is moved upward, and then, the wheel tip 110 can beexchanged.

Names and functions of elements having no reference numeral or elementshaving only reference numerals will be readily apparent from otherdrawings and descriptions thereof in this specification.

As can be seen from the foregoing, a wafer polishing apparatus inaccordance with the technical sprit of the inventive concept canaccomplish the following effects.

First, as the exchange period of the wheel tip is lengthened and thenumber of exchanges of wheel tips is reduced, it is possible to reducethe number of dressing processes for adjusting an initial polishing loadupon exchange of the wheel tip, and thus, the time consumed for qualitystabilization can be absolutely reduced.

Second, since only the wheel tip is exchanged, with a wheel shankremaining, it is possible to reuse the wheel shank to reduce overallfabrication costs.

The foregoing is illustrative of example embodiments and is not to beconstrued as limiting thereof. Although a few example embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in example embodiments withoutmaterially departing from the novel teachings and advantages.Accordingly, all such modifications are intended to be included withinthe scope of this inventive concept as defined in the claims. Therefore,it is to be understood that the foregoing is illustrative of variousexample embodiments and is not to be construed as limited to thespecific embodiments disclosed, and that modifications to the disclosedembodiments, as well as other embodiments, are intended to be includedwithin the scope of the appended claims.

1. A wafer polishing apparatus comprising: a spindle shaft rotated by amain motor; a wheel shank axially and rotatably coupled to the spindleshaft; a moving shaft engaged with the spindle shaft by a gear to berotated; and a wheel tip coupled to the moving shaft and supported bythe wheel shank, constructed and arranged to polish a wafer.
 2. Thewafer polishing apparatus according to claim 1, wherein the gearcomprises: a screw jack coupled to the moving shaft and having a femalethread; and a lead screw coupled to the spindle shaft by a bearing andhaving a male thread.
 3. The wafer polishing apparatus according toclaim 2, further comprising a step motor supported by the spindle shaft,and rotating the lead screw to straightly move the moving shaft withrespect to the spindle shaft in a vertical direction.
 4. The waferpolishing apparatus according to claim 2, wherein the wheel shankcomprises: a spindle coupling part axially coupled to the spindle shaft;and a cover part having a slide groove in which the wheel tip issupported or slid.
 5. The wafer polishing apparatus according to claim2, wherein the moving shaft comprises: a connecting part to which thescrew jack is integrally coupled; and a slide part extending to a lowerpart of the connecting part and under which the wheel tip is mounted. 6.The wafer polishing apparatus according to claim 5, wherein: the spindleshaft comprises a plurality of connecting holes extending in an axialdirection thereof, and the connecting part is connected within thespindle shaft in a cross shape, and slid along the connecting hole in anaxial direction thereof.
 7. A wafer polishing apparatus comprising: arotatable spindle shaft; a wheel shank integrally fixed to the spindleshaft; a moving shaft variably fixed to the spindle shaft; and a wheeltip detachably mounted on the moving shaft.
 8. The wafer polishingapparatus according to claim 7, wherein: the wheel shank comprises aslide hole configured to conceal the wheel tip other than an exposedportion of the wheel tip in direct contact with a wafer, and the movingshaft comprises a slide part slid in the slide hole together with thewheel tip.
 9. The wafer polishing apparatus according to claim 8,wherein the slide part further comprises an attachment groove positionedat a first end and to which the wheel tip is detachably attached, andthe attachment groove has an open lower end so that the wheel tip can beinserted in an upward direction with respect to a longitudinalcross-section thereof.
 10. The wafer polishing apparatus according toclaim 9, wherein: the slide part further comprises a fastening holepassing through both sides thereof and at least the attachment groove;and a bolt is fastened to the fastening hole to fix the wheel tipinserted into the attachment groove.
 11. A wafer polishing apparatuscomprising: a wheel tip constructed and arranged to be in direct contactwith a wafer; a spindle shaft configured to receive power to enablerotation of the wheel tip; a wheel shank positioned at a lower part ofthe spindle shaft and supporting the wheel tip, the wheel tip not beingdirectly fixed thereto; and a moving shaft having a first side on whichthe wheel tip is mounted and a second side to which the spindle shaft isconnected, and relatively movable with respect to the spindle shaft. 12.The wafer polishing apparatus according to claim 11, wherein the wheelshank comprises: a spindle coupling part coupled to the spindle shaft atan upper center thereof; and a cover part configured to expose a portionof the wheel tip at a lower edge thereof.
 13. The wafer polishingapparatus according to claim 12, wherein the wheel tip has a width W of3 mm to 4 mm and a height H of 5 mm to 15 mm, and a height H1 of thewheel tip exposed from the cover part is maintained within a range of 1mm to 4 mm.
 14. The wafer polishing apparatus according to claim 12,wherein: the cover part further comprises a slide hole through which thewheel tip can vertically pass, and as the slide part is slid downwardfrom the slide hole, a height H2 of the wheel tip concealed by the coverpart is reduced, and the height H1 exposed from the cover part isuniformly maintained within the range.
 15. The wafer polishing apparatusaccording to claim 14, wherein the slide hole corresponds to a shape ofthe wheel tip, and has a step between upper and lower parts thereof sothat a hole gap at the upper part is larger then the thickness of thewheel tip, and a hole gap at the lower part is equal to or approximateto the thickness of the wheel tip with respect to a longitudinalcross-section thereof.
 16. The wafer polishing apparatus according toclaim 15, wherein: a vertical surface of the step is a surfaceconfigured to support the wheel tip, and a horizontal surface of thestep comprises a stopper surface to prevent the moving shaft fromlowering any further.
 17. The wafer polishing apparatus according toclaim 11, wherein the moving shaft comprises: a connecting part movablyconnected to the spindle shaft; and a slide part to which the wheel tipis detachably attached.
 18. The wafer polishing apparatus according toclaim 17, further comprising a variable means configured to fix themoving shaft to the spindle shaft during polishing or to vary a positionof the moving shaft when the wheel tip is worn down.
 19. The waferpolishing apparatus according to claim 18, wherein the variable means isa screw gear assembly, and the screw gear assembly comprises: a screwjack formed at the moving shaft; a lead screw connected to the spindleshaft and passing through the screw jack; and a step motor configured torotate the lead screw, wherein when the lead screw is rotated by thestep motor, the screw jack moves longitudinally in a vertical directiondepending on a rotational direction of the lead screw.
 20. The waferpolishing apparatus according to claim 18, wherein the variable means isa linear actuator, and the linear actuator comprises: a piston rodextending to be connected to the connecting part in a cross shape; and alinear step motor configured to move the piston rod in a longitudinaldirection thereof, wherein when the linear step motor is driven, thepiston rod moves longitudinally in a vertical direction.